I. Field of the Invention
This invention relates to a magnetic recording medium. More particularly, this invention relates to a magnetic recording medium of the type in which a magnetic layer is coated on a substrate film.
II. Description of the Related Art
Magnetic recording media of the type in which a magnetic layer is coated on a substrate film (hereinafter referred to as "coating type magnetic recording media") are known. A coating type magnetic recording medium is described in, for example, U.S. Pat. No. 4,684,546, which discloses a magnetic recording medium comprising a polyester film and a magnetic layer coated on the film.
In the conventional coating type magnetic recording media, the surface of the magnetic layer is made as smooth as possible in order to promote the S/N ratio (signal to noise ratio) in high density recording (The higher the S/N ratio, the better the quality of the recorded information, such as recorded images when the recording medium is a video tape). However, the smoother the surface of the magnetic layer, the higher the friction coefficient when the recording medium runs. Since higher friction coefficient more severely damages the recording medium, the durability of the recording medium having a magnetic layer with such a smooth surface is low, so that the high S/N ratio is sharply decreased when the magnetic recording medium is repeatedly used. On the other hand, if the surface of the magnetic layer is roughened in order to promote the durability, the S/N ratio is decreased. Thus, the effort to promote the S/N ratio impairs the durability of the recording medium, and vice versa.